The objective of the proposed research is to characterize the mechanism(s) by which a class of organotin compounds, butyltins (BTs), inhibit the cytotoxic function of human natural killer (NK) cells. The hypothesis that BT-induced decreases in cAMP and ATP are at least in part responsible for inhibition of NK cytotoxic function will be investigated. NK cells are able to destroy tumor cells and virally infected cells without prior sensitization putting them at the forefront of our immune defense against such cells. There is significant exposure of humans to BTs from a variety of sources. Further, BTs have been shown to increase the risk of cancers and viral infections in exposed individuals. A possible route by which BTs may increase the risk of cancers and viral infections is by their inhibition of the eytotoxic function of NK cells. Data are presented showing that BTs can dramatically decrease intracellular cAMP levels as well as significantly decrease levels of important cell surface molecules and proteins of the cytotoxic granules in NK cells. A 24 h exposure to BTs also significantly decreases ATP levels in NK cells. Determination of the mechanism(s) by which BTs diminish NK cell function is an important factor in determining the overall mechanism by which they may be increasing cancer incidences in exposed populations. The specific aims of this research are: 1. Determine the role of decreased cAMP levels in the BT-indueed inhibition of NK cytotoxic function by comparing the effects of BT exposure; adenylyl cyclase (AC) inhibitors; and cAMP-dependent protein kinase (PKA) inhibitors on cytotoxic function (S_Cr release assay) and on enzyme activities essential to the cytotoxic response. 2. Determine the effects of BT exposure; AC inhibitors; and PKA inhibitors on expression of NK-cell surface molecules, using flow cytometry. 3. Characterize the effects of BT exposure; AC inhibitors; and PKA inhibitors on levels of cytolytic molecules (granzyme and perforin). 4. Determine the effects of BT exposure; AC inhibitors; and PKA inhibitors on the phosphorylation state of the transcription regulator(s), cAMP response element binding protein(s) (CREB). 5. Characterize the effects of decreased ATP levels in inhibition of NK cytotoxic function following a 24 h exposure to BTs, using ATP synthesis inhibitors.